1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays).
2. Description of the Prior Art
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/(I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. Particularly, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, the photoconductive material which is attracting attention in recent years is an amorphous silicon (hereinafter referred to as a-Si) in which dangling bonds are modified with mono-valent elements such as hydrogen or halogen atoms. For example, German OLS Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German OLS No. 2933411 discloses an application of a-Si for use in a photoelectric transfer reading device. Such an amorphous silicon is expected to be applied for an image forming member for electrophotography due to its excellent photoconductivity, friction resistance, heat resistance and relative easiness in enlargement of area.
Generally speaking, in preparation of a photosensitive drum for electrophotography having a photoconductive material containing a-Si, in order to obtain good photoconductive characteristics, a-Si deposited film is formed on a drum-shaped substrate under the condition wherein the substrate is heated to a temperature of 200.degree. C. or higher in a a-Si film deposition device.
However, because of the difference in coefficient of thermal expansion between the drum-shaped substrate and the a-Si film and also because of the great internal stress within the a-Si film, not only during deposition of the a-Si film when the drum-shaped substrate is heated as described above, but also during cooling after deposition, it is frequently recognized that the a-Si film is peeled off from the drum-shaped substrate.
According to a large number of experiments by the present inventors, such peeling of the film will occur more readily as the a-Si film is thicker. Also, even by deformation of the drum-shaped substrate to the extent which will not cause peeling in a Se type photosensitive drum for electrophotography of the prior art, peel-off of the film may be caused in the case of the a-Si photosensitive drum for the reasons as mentioned above, namely difference in coefficient of thermal expansion and greatness of internal stress within the a-Si film. As to the internal stress in the a-Si film, it can be alleviated to some extent by the preparation conditions of a-Si film (starting gases, discharging power, temperature for heating substrate, etc.). However, such a peel-off of the film is a vital disadvantage, causing image defect when employed as the photosensitive drum for electrophotography.
Also, heating of the drum-shaped substrate during preparation of a-Si film is not only a cause for the above film peel-off, but also generates readily thermal deformation of the drum-shaped substrate. The thermal deformation will cause unevenness in discharging during preparation of a-Si deposited film, whereby evenness in thickness of the a-Si deposited film is lost and image defect may be brought about.
The present invention has been accomplished in view of the various points as mentioned above, and as the result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid stage image pick-up devices, reading devices, etc., it has now been found that the above problems such as film peel-off can be overcome by use of a drum-shaped substrate having a specific thickness as the support for the a-Si deposited film.